What you're really asking here is "should I try building a piece of furniture". So it all depends on a few things.

I've built a number of custom units for computers and whatnot, but then, I have access to routers, table saws, etc. I find that if you know your way around basic tools, and you spend some time thinking about exactly what it is you want, checking out how the professionals put things together, etc., you shouldn't have much trouble. The final appearance is the variable. I've learned (yes, the hard way) that there's a reason the professionals are called "professionals"; they know what looks good an what doesn't. That in mind, I would recommend starting with an existing design, and modifying it to fit your needs.

I would recommend against using parts of other furniture. Not only are you combining things that weren't meant to be combined, but you'll have a hard time getting it to look like a cohesive whole.